Self-test arrangement for an entertainment-service system

ABSTRACT

In an entertainment-service system for permitting each of a plurality of local stations to select one or more of a plurality of channels of audio signals and to control one or more utilization circuits associated with each local station or group of such stations through the application of multiplexing techniques, the improvement consisting of a self-test arrangement whereby a test signal of predetermined characteristics is applied to each input channel of the multiplexing means and a self-test circuit means is provided at each station to detect said test signal and to override the control for said utilization circuit to activate said utilization circuit in a unique mode.

United States Patent [72] Inventor David R.Greenberg Old Bethpage, N.Y.

[21] Appl. No. 800,941

[22] Filed Feb. 20, 1969 [45] Patented June 15, 1971 [73] Assignee Instrument Systems Corporation Huntington, N.Y.

[54] SELF-TEST ARRANGEMENT FOR AN ENTERTAINMENT-SERVICE SYSTEM Prirriary ExaminerRalph D. Blakeslee Attorney- Blum, Moscovitz, Friedman and Kaplan ABSTRACT: In an entertainment-service system for permitting each of a plurality of local stations to select one or more of a plurality of channels of audio signals and to control one or more utilization circuits associated with each local station or group of such stations through the application of multiplexing techniques, the improvement consisting of a self-test arrangement whereby a test signal of predetermined characteristics is applied to each input channel of the multiplexing means and a self-test circuit means is provided at each station to detect said test signal and to override the control for said utilization circuit to activate said utilization circuit in a unique .mode.

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SHEET 5 BF 8 ATTORNEYS ATENTEU JUNI 5 IHYi SHEET 7 OF 8 IN VILYIIIK 64%;, ATTORNEYS PATENTEH JUN] 5 Ian SHEET 8 0F 8 BACKGROUND OF THE INVENTION This invention relates generally to entertainment-service systems of the type applicable to a plurality of remote stations such as might be found in aircraft. The testing of such systems generally requires the separate operation of each component. Thus, if the system included a plurality of demultiplexers each servicing a group of remote stations, each of said stations being provided with a separate headset, the prior art method of testing such a system would consist of individually listening at each headset to detect an audio input. Substantially all of the entertainment portion of such a system would be tested in this manner provided that at least one of the channel selection means in the system is set to each of the channels. To test the service portion of such a system, it would be necessary to individually operate the utilization control means at each station and detect the results at the corresponding utilization circuit.

The above-described testing method is extremely time consuming, a factor which is of particular importance where the conduct of a lengthy test would substantially increase the down time of an otherwise available aircraft.

SUMMARY OF THE INVENTION Generally speaking, in accordance with the invention, a self-test arrangement for an entertainment-service system is .provided. The entertainment-service system to which the selftest arrangement according to the invention is to be applied includes an entertainment portion wherein a plurality of channels of input are multiplexed and transmitted as a single signal to a plurality of remotely located demultiplexer means which reconstruct the content of the input channels selected by a channel selector means associated therewith and transmit said reconstructed signal to a corresponding transducer means. The service portion of the system to be tested includes a plurality of remotely located utilization circuits, at least one utilization control means associated with each of said utilization circuits and means for placing each of said utilization circuits in astate responsive to the state of its corresponding utilization control means. The self-test arrangement consists of a multichannel test signal generator connected to the multiplexing means to apply a test signal of a predetermined characteristic to each input channel and at least one self-test circuit means connected to the output of each demultiplexer means to detect the presence of said test signal and to override, in response to said detector test signal, at least one utilization control means to produce a unique state indication at said utilization control means effective to operate the corresponding utilization circuit in a uniqlie manner. The unique state indication may correspond to that which would be produced if the utilization control means were alternately turned on and off so that the corresponding utilization circuits are alternately rendered operative and inoperative when said test signal is detected.

The self-test circuit includes filter means adapted to pass a signal of a frequency substantially identical to the frequency of the test signal, transducer sense means adapted to produce a further signal if the transducer means coils are intact, an AND" gate to receive the signals of said filter means and transducer sense means and switch means to override the utilization control means in the manner described above.

Accordingly, it is an object of this invention to provide a test arrangement for an entertainment-service system which requires a minimum of additional test equipment and which permits the rapid testing of the system.

Another object of the invention is to provide a testing arrangement for an entertainment-service system which permits ready diagnosis of any defects therein.

A further object of the invention is to provide a testing arrangement-which permits the testing of an entertainment-service system through the inclusion of a compact testing module within each local control of said system and appropriate signal test generators.

Another object of the invention is to provide a testing arrangement for an entertainment-service system which permits the simultaneous testing of substantially the entire system.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic representation of one type of entertainment-service system according to the invention;

FIG. 2 is a schematic representation of the main multiplexer of said entertainment-service system;

FIG. 3 is a schematic representation of the local demultiplexer of said entertainment-service system;

FIG. 4 is a schematic representation of the local control of said entertainment-service system including the self-test circuit for said system;

FIG. 5 is a circuit diagram of one type of the self-test circuit of FIG. 4;

FIG. 6 is a schematic representation of the column timer,

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, the entertainment-service system depicted utilizes multiplexing techniques, preferably of the pulse code modulation type, to permit a plurality of local stations to selectively receive one or more of a plurality of channels of audio signals and to control one or more utilization circuits associated with each local station or a group of such stations. Pulse code modulation is a form of time division multiplexing wherein the time available to transmit a plurality of channels of information is divided into a plurality of discrete intervals or frames which are assigned successively to each of said channels. Each channel of information to be transmitted is successively sampled and the analog value thereof is converted to a digital pulse code. Each of said intervals or frames are in turn divided into time slots, one of said time slots being assigned to each bit of the digital code. Further time slots can be assigned for the transmission of other information, if desired. In this manner a plurality of channels of information may be transmitted over a single line and reconstructed at the receiver to produce the plurality of channels of information originally transmitted.

In particular, in the system according to the invention, an audio input 10, for example having ten channels, feeds into a main multiplexer 12. Said main multiplexer originates the basic system timing, multiplexes the input signals by sequentially sampling each of the channels and converting the analog signals todigital form, and transmits along line 13, the resulting digital data along with clock and synchronization signals in the form of a train of pulses, to the zone submultiplexers 14. In the embodiment shown in FIG. I, five further channels of audio input 16 are applied to each zone submultiplexer 14. Each of said zone submultiplexers function in a similar manner to main multiplexer 12 to multiplex said five additional channels and to interleave the resulting digitized multiplexed signal in the'appropriate frames of the main multiplexer output signal. The timing and sampling arrangements of said main multiplexer are adapted to provide the additional frames required in each cycle to permit the addition of the further five channels of audio input by each zone submultiplexer 14.

The output of each zone submultiplexer 14, which consists of fifteen channels of multiplexed information is applied to a single line 17. Reconstruction of the multiplexed signal for the remotely located stations is performed by a plurality of local demultiplexers 18, each of which taps its respective line 17, reconstructs the multiplexed signal into its component channels of analog audio signals and transmits to its corresponding headsets 20 disposed at each remote station the particular channel selected by the local control 22 (22A, 228 or 22C) associated therewith. In this manner, a plurality of audio channels are transmitted to a plurality of stations represented by local controls 22 and headsets 20 associated therewith. Each of said stations can be remotely located relative to the audio inputs and 16, main multiplexer 12 and zone submultiplexer 14, while requiring only a single channel for information transmission, and therefore a minimum of wiring. Despite the use of a single channel for transmission, each local control 22 can select one or a pair of said channels (as in the case of stereo transmissions) to provide the user at the remote station with an accurate reproduction of the audio signal from the multichanneled input 10 and 16.

Local controls 22 are also adapted to permit each remote station to control, through the application of multiplexing techniques, a local utilization circuit 24 (24A, 248 or 24C) associated therewith. Such local utilization circuit might include, for ample, service call lights, other fonns of attentionattracting alarm means, or lamps for general illumination or reading.

For this purpose, column timer 26, a plurality of local coders 28 (28A, 28B,...,28l( and a corresponding number of local decoders 30 (30A, 30B,...,30K) are provided. Column timer 26 is adapted to produce the basic timing for this portion of the system, transmitting a clock and synchronization signal along data line 32 which interconnects said local coders.

Each cycle is divided into frames, one frame being allotted to each local coder-decoder pair. Each frame is in turn divided into time slots allocated to each function to be performed such as the state of the portion of local control 22A which governs the service call light in local utilization circuit 24A or the state of the portion of local control 22C which governs the light in local utilization circuit 24C. Data is transmitted in the form of a train of pulses, the presence or absence of a pulse in each time slot governing the corresponding function. Each of said local coders are identical and adapted, when activated, to detect the state of the local controls associated therewith and to transmit digital data identifying said state to data line 32 during predetermined time slots and frames. In like manner, each of said local decoders are identical and are adapted to query said data line during predetermined time slots and frames to detect the local control state data transmitted by the corresponding local coder, and to operate the local utilization circuits 24 associated therewith, so that they are disposed in accordance with the settings oflocal controls 22.

Activation of local coder 28 and local decoders 30 in the appropriate time frames is accomplished in response to the clock and synchronization signal generated by column timer 26 which is also transmitted along shift lines 34 which connect said column time and local coders 28 in series and shift lines 36 which connects said column timer and local decoders 30 in series. The signal transmitted along shift lines 34 and 36 sequentially activates local coders 28 and local decoders 30 respectively so that for example, only local coder 28B and its corresponding local decoder 308 are activated during the second time frame, and therefore transmit and receive during that frame.

Column timer 26 may also be adapted to perform supervisory coder and decoder functions by querying data line 32 at predetermined time slots to detect local control state data contained therein for the activation of a centrally located supervisory utilization circuit 38 and to transmit to said data line, during predetermined time slots, digital data representative of the state of a supervisory control 40.

The embodiment of the entertainment-service system according to the invention shown in FIG. 1 incorporates zone submultiplexers 14 to introduce further channels of audio input 16. Such further channels would be required if it were necessary to provide a number of channels of unique audio input at each zone, as would be the case where movies were being projected at each zone and synchronization between sound track and film required separate transmission of said sound track at each zone. However, where such separate transmission is not required, the audio input 16 and zone submultiplexers 14 may be dispensed with in the entertainmentservice system according to the invention. ln such embodiments, local demultiplexers 18 would tap directly off line 13 to receive the output of main multiplexer 12.

Further, in the embodiment of the system shown in FIG. 1, one column timer 26 is provided for the group of local stations associated with each zone. However, depending on the number of local stations, the switching speed of the equipment, and the frequency with which each station must be scanned, a single columntimer 26 may be utilized to control all of the local coders 28 and local decoders 30 in the system, without regard to the one in which they may fall. In the alternative, more than one column timer might be utilized to control the local coders 28 and-local decoders 30 in each zone, provided that each local coder and its corresponding local decoder are tied to only a single column timer. As shown by dashed lines 8, each line 17 would be provided with a complete set of local demultiplexers 18, local controls 22, local coders 22, a column timer 26, etc.

Turning now to a more detailed discussion of the components of the entertainment-service system according to the invention, reference is had to FlG. 2 which shows a schematic representation of the main multiplexer 12. The ten channels of audio input 10 are applied to 10 amplifiers and filters 42, the output of which is applied to an electronic commutator 44. The timing for the audio portion of the system is obtained from crystal clock oscillator 46 which is applied to system control logic and timing counters 48. Said system control logic and timing counters control the operation of the main multiplexer by providing the gating signals to insure proper synchronization and sequential timing of the components. Thus, 10 lines 50 connect system control logic and timing counters 48 to commutator 44 to enable said commutator to sequentially sample each of the 10 input channels during a predetermined time frame. Since the entire system, as shown in FIG. 1, would include 15 channels, the system control logic and timing counters would actually divide a single cycle into 15 time frames, only 10 of which are utilized by the commutator 44 of the main multiplexer. The remaining five time frames are preserved for the five additional channels to be introduced by each zone submultiplexer 14. The number of channels of the embodiment shown in the drawings is given by way of example and not by way of limitation, the actual number of channels in an entertainment-service system according to the invention being a matter of selection.

During the frame that each channel is being sampled, the sampled signal is applied to sample and hold circuit 52 which is also controlled by system control logic and timing counters 48 through an enable line 53 and a reset line 54. The held sample is applied through a driver 55 to comparator $6 of analogto-digital converter 58 of conventional design. The timing for analog to digital conversion is also controlled by system control logic and timing counters 48. In the embodiment shown, analog-to-digital conversion is performed by an 8-bit ladder network 60 which generates a series of voltages for application to comparator 56 through a driver 62. Said voltages are matched by said comparator to the sampled audio signal. The ladder network 60 is controlled by a conversion register 64 whose operation is in turn governed by a conversion control logic 66 responsive to system control logic and timing counters 48. When comparator 56 detects a match between the audio signal and the voltageoutput of the ladder network 60, a signal applied along line 68 to conversion control logic 66 causes conversion register 64 to transmit the digital code corresponding to the matched voltage along line 69 to data output logic 70. Said data output logic assembles the various components of the main multiplexer output signal with each bit in its assigned time slot and transmits said output signal through low impedance driver 72 to line 13, shown as a coaxial cable, for transmission to the various zone submultiplexers 14. Timing for data output logic 70 is also provided by system control logic and timing counters 48 through data timing lines 73.

The output signal from main multiplexer 12 consists of a periodic clock and frame synchronization signal having the digital data representing the audio signal in each channel interleaved therein, and is in the form of a train of pulses. The clock and frame synchronization pulses are provided directly to data and input logic. 70 by system control logic and timing counters 48 through clock and frame sync line 74.

In some applications, it is desirable to provide a single channel of input, the activationof which overrides the other channels so that only the content of that channel is transmitted to headsets irrespective of the channel selected by local control 22. Thus, it would be desirable to have the channel set aside for a public address system function in this manner. To this end, an override bit is transmitted by system control logic and timing counters 48 in an appropriate time slot in each frame to data output logic 70, along. line 77 for interleaving in the output pulse train. Said override bit is generated in response to the activation of said predetermined channel as by PA selector switch 75. Upon detection of such override bits, local demultiplexers 18 transmit only the channel assigned to the public address system. i

Still a further feature of the main multiplexer according to the invention is the provision of stereo/monaural selector switches 76. These selector switches introduce a stereo tag bit into a predetermined time slot of the frame assigned to the first of two adjacent channels carrying the left and right components of a stereo signal. When local demultiplexer 18 detects such a stereo tag, it will apply one of said pair of channels to the left and the other to the right side of headset 20, treating said two adjacent channels as a single channel for the purpose of channel selection by local control 22. This feature greatly increases the flexibility of the system since no channels are permanently dedicated to stereo transmission.

Each of the zonesubmultiplexers 14 operates in substantially the same manner as main multiplexer 12. The frame synchronization and clock signal utilized to regulate the system control logic and timing counters of the zone submultiplexers is stripped from the signal on line 13, although each of said zone submultiplexers can be provided with an auxiliary crystal clock oscillator, if desired, to provide a standby timing source in case of failure of the main multiplexer. In other.

respects, the zone submultiplexers preferably include system control logic ano timing counters, commutator, sample and hold circuit, analog-to-digital converter and data output logic similar in function and structure to the corresponding components of the main multiplexer but adapted to interleave the digitized lots corresponding to the five channels of audio input 16 in the appropriate frames and time slots reserved therefore and to pass the thus modified signal from line 13 to its respective zone line 17, which is also preferably a coaxial cable.

The signal from each zone line 17 is tapped off by the corresponding local demultiplexers 18, a schematic representation of one of which is shown in FIG. 3. The signal tapped from line l7is amplified by high impedance amplifier 78 and applied to shaper 80 adapted to eliminate any spurious signals. The frame synchronization and clock portions of the signal are detected by sync and clock detector 82 which applies these portionsof the signal to the system control logic and timing counters 84 which control the timing and operation of the remaining components of the local demultiplexer. The clock signal drives the counters and logic while the frame synchronization is used to lock the system timing to that of zone submultiplexer 14 and main multiplexer 12. The signal from shaper is also applied to the data input logic and conversion control 86 of digital-to-analog converter 88. This signal includes, sequentially, the digitized instantaneous value of each of the input channels audio signal plus stereo tag bits, if any. As each data bit is received, the corresponding flip-flop in the conversion register 90 is set to that data bit condition which in turn sets the 8-bit digital-to-analog ladder network 92 to the original sample audio values. This ladder network analog voltage is applied through driver 94 to a plurality of sample and hold networks 96 (96A-1, 96A-2'. 968-1, 968-2, 96C-1, 960-2). One of said sample and hold networks are associated with each audio output circuit, two of said audio output circuits being provided for each station (headset 20 and local control 22), whereby each station is provided with full stereo capability.

The system control logic and timing counters 84 provide timing signals through lines 98 to channel selection logic 100. Said channel selection logic also receives the stereo tag, it any, from the data input logic and conversion control 86 along line 102 to determine whether a single channel of information should be applied to both audio output circuits associated with a single station or whether one of a pair of adjacent channels of information should be applied to each of said two audio output circuits to produce a stereo effect.

Each of said sample and hold circuits 96 drives an active low-pass filter 104, which drives into an amplifier I06 connected at its output to capacitor 108, which in turn is connected to the audio output line 110. Each pair of audio output lines ll0A-1 and 110A-2, 1108-1 and 1108-2, and 1l0C-1 and l10C-2, are connected to one of said local controls 22 (22A, 22B and 22C respectively) which contain channel selection means and headset 20 which is operated by the signal from said audio output lines.

Channel selection logic detects the setting of each local control 22 by means of lines 112A, 1128 and 112C connected respectively to audio output lines 1l0A-1, 1103-1 and l10C-l in a manner to be described below. In response to the signal from said lines 112A, 1123 and 112C, channel selection logic gates each sample and hold circuit 96 into and out of operation during the time frame corresponding to the channel selected at the respective local control. This gating signal is sent along sample lines 1l4A-1, 114A-2, 1148-1, 1143-2, 1l4C-1 and 114C-2. Thus, if local control 22A were set to select a stereo program, that fact would be detected by channel selection logic 100 through line 112A. Based on the system timing derived along lines 98, said channel selection logic would gate sample and hold circuit 96A-1 to sample and hold the output of amplifier 94 during the time frame assigned to the first of the pair of stereo channels selected while sample and hold circuit 96A-2 would be gated to sample and hold during the time frame assigned to the second of said pair of stereo channels. If a monaural channel is selected at local control 22A, sample and hold circuits 96A-1 and 96A-2 would be simultaneously gated to sample and hold the output of amplifier 94 during the same time frames, whereby the same audio signal is transmitted to both sides of headset 20.

Filters 104 are selected to pass only audiofrequencies and to have a sharp attenuation characteristic to produce an audio output. This audio output is applied along each audio output line 110 to its corresponding local control 22.

A block diagram of one of local controls 22 is shown in FIG. 4. The channel selection means 116 of said local control consists of a single pole multiple position rotary switch. Movable arm 1180f said switch selectively engages one of a plurality of fixed contacts 120 which are connected through resistors 122 to ground. Said movable arm is connected by means of line 123 to audio output line ll0A-1, and therefore to line 113A of local demultiplexer 18, which in turn is connected to channel selection logic 100 for the purpose of detecting the state of said channel selection means.

Audio output line l10A-1 is also connected to capacitor 124 which in turn is connected to the input of rheostat 125. Audio output line 110A-2 is connected through capacitor 126 to the input of rheostat 127. The left and right transducers, 128 and 130 respectively, shown schematically, are connected between the wipers of said rheostats 125 and 127, respectively and ground. In this manner, the audio signal, whether stereo or monaural, is applied to the coils of transducers 128 and 130 which convert the electrical signal to sound for application to headsets 20. Adjustment of the rheostats 125 and 127 adjusts the volume of the signal applied to said headsets. Channel selection means 116 is shown in FIG. 4 with a lZ-position switch, in which case several of the input channels of audio would be stereo pairs automatically selected by one position on said channel selection means.

Each of said resistors 122 are of a different value. The selected resistor serves as a part of a voltage divider located within channel selection logic 100 of local demultiplexer 18. The output of said voltage divider is filtered to DC within said channel selection logic which is preferably provided with a ramp sweep generator and comparator. When said comparator matches the output of said ramp sweep generator with the output of said voltage divider as determined by the setting of movable arm 118, the comparator activates logic circuitry within channel selection logic 100 which, preferably through a digital code, identifies the selected circuit. As mentioned above, channel selection logic 100 is adapted to detect the stereo tag, if any,-in which case two adjacent channels of stereo would be treated as a single program selected by a single position of selection switch 116. The foregoing arrangement permits the seat selection function to share one of each pair of audio output lines 110, thereby avoiding an additional cable extending between each local demultiplexer 18 and its corresponding local control 22.

Turning now to the service portion of the system, an example of a column timer 26 and the supervisory utilization circuit 38 and supervisory control 40 associated therewith is shown in FIG. 6. Basic timing for this portion of the system is obtained by crystal clock oscillator 130 which provides a stable frequency source which drives timing counters 132 to produce system clock and frame synchronization pulses and to govern the operation of data output logic 134. Such clock and sync pulses are included in the train of pulses forming the output of data output logic 134 which is transmitted along line 135 to driver 136. This output signal is applied to data line 32 and shift lines 34 and 36. As discussed above, shift line 34 is connected to the first local coder 28A while shift line 36 is connected to the first local decoder 30A. This output signal is divided by the clock and sync pulses into a plurality of frames, each assigned to a particular local coder and its corresponding local decoder. Each of said frames is subdivided and time slots therein are assigned to each of the functions to be performed by the service system. The data in each time slot is generally applied by local coders 28 in response to the settings of the corresponding local controls 22. However, it is sometimes desired to provide supervisory control functions at a control location, in which case a supervisory control circuit 40 of the type shown in FIG. 6 might be connected to data output logic 134, which would then interleave in the appropriate time slots, as governed by timing counters 132, data responsive to the settings of said supervisory control.

In the embodiment shown in the drawings, the service portion of the system is adapted by way of example, to perform two functions, namely to activate a lamp associated with each local control and to activate a service call light associated with each group of three local controls. The supervisory control shown in FIG. 6 serves both a test and a functional purpose ,and consists of a three-position lamp test switch 138, a twoand 146. When first conEct 144 is engaged, data output logic 134 transmits the data required to turn all lamps in all local utilization circuits 24 on. When second contact 145 is engaged, data output logic 134 interleaves the data in the appropriate time slots of the output signal direction all lamps in all utilization circuits to be turned off, third contact 145 being a neutral position.

Service call light test switch 140 includes a movable arm 146 normally engaged to neutral fixed contact 147, but displaceable into engagement with the other fixed contact 148, in which case data output logic 134 will interleave into the pulse stream, the appropriate data necessary to activate all service call lights of all of said local utilization circuits. Reset call light switch 142, when depressed, causes data output logic 134 to interleave into the data stream in the appropriate time slots the data necessary to reset all of the service call lamps of all of said local utilization circuits. Also included are switches 166 and 168 which control the test signal generators utilized in the self-test feature of the system in a manner to be described below.

The embodiment of the system shown in the drawings also includes a supervisory utilization circuit 38, which is shown in FIG. 6 to include a supervisory chime 150 and a supervisory call light 152. To this end, column timer 26 is preferably provided with data input logic 154 which taps data line 32 by means of line 156. The timing of said data input logic is governed by timing counters 132 through line 157. If data input logic 154 detects that any one of the local controls 22 is set to enable its corresponding call light in its corresponding utilization circuit to light, a signal is passed along lines 158 to flip-flop 160, the output of which is connected to supervisory call light 152 through amplifier 162. Flip-flop 160 serves to latch the supervisory call light in the on position until all of the call light controls in all of the local controls 22 are reset. The affirmative act of resetting is required to insure that appropriate action is taken in response to each service call light. As a further alarm means in connection with the service call light, the activation of the service call light control at a local control 22 also results in the transmission by the local coder in the appropriate time slot of a pulse directing the ringing of supervisory chime 150. This pulse is detected by data input logic 154 to pass a signal along line 163 to single shot multivibrator 164 the output of which is connected to said supervisory chime through amplifier 165. The frequency and duty cycle of said single shot multivibrator 164 is selected to limit the frequency with which the chime rings.

As shown in FIG. 4, each local control 22 includes a manual lamp control operative through switch means 174 to impress a signal on line 176, which in turn in connected to its corresponding local coder 28. Similarly, each local control 22 is provided with service call light and chime control 178, which, when depressed, closes contacts 179 to pass first signal along line 180 to said corresponding local coder, and when raised, closes contacts 181 connected in series with resistance 182 to pass a second, different, signal on line 180. Preferably, said first signal represents a command to light the corresponding service call light and ring the supervisory chime, while said second signal directs the resetting of said corresponding service call light.

As seen in FIG. 7, which schematically represents one example of a local coder 28 according to the invention, lines 176 and 180 from the lamp control 170 and service call light and chime control 178 respectively of each local control 22A, 22B, 22C are applied to the date output logic 183 thereof. Timing for local coders 28 is obtained by means of sync and clock detector 184, preferably a chain of single shot multivibrators, which taps off data line 32 and strips the clock pulses from the pulse train. The clock and frame synchronization pulses are passed to timing counters 186 along clock and reset lines 185. Said timing counters control the functioning of data output logic 183 through lines 187 but are inhibited from driving said data output logic until a shift-in command is received from shift line 34 connected to the last local coder, or in the case of the first local coder 28A, connected to the column timer 26. This shift command consists merely of the sync and clock pulse and operates as follows. The frame synchronization pulse resets all of the timing counters 186 in all of. the local coders 28A, 28B,...,28K, enabling the timing counters on the first local coder to respond to the clock pulses received from column timer 26 along shift line 34. When the timing counters 186 of said first local coder 28A have completed their cycle and directed data output logic 183 thereof to transmit the state data of the corresponding local controls 22, a shift-out command is generated by said timing counters and passed along shift line 34 to the timing counters of the second local coder 28B which is then activated to function as described above. This sequential activation of the local coders continues until the last local coder 22K has completed its cycle, at which time a frame synchronization pulse resets the entire portion of the system and a new cycle is commenced.

During the period that each local coder is activated, data output logic 183 detects the states of local controls 22A, 22B and 22C and, during appropriate time slots, transmits data representative of said states through low impedance driver 188 to data line 32. The sequential activation of said local coders insures that the data is interleaved into the proper frame for detection by the corresponding local decoder 30.

Local coders 30, a schematic representation of one example of which is shown in FIG. 8, are designed to be sequentially activated in the same manner as said local coders. Thus, the pulse train is tapped off data line 32 and applied through driver 190, to sync and clock detector, 192 and data input logic 194. Reset and clock pulses are applied from said sync and clock detector to timing counters 195 which are governed by shift commands from shift lines 36. Sync and clock detector 192, timing counters 195, and shift lines 36 function in the same manner as sync and clock detector 184, timing counters 186 and shiftlines 34 of local coders 22, and a detailed description of their operation will not be repeated at this point. The operation of data'input logic 194 is governed by timing signals obtained from timing counters 195 along lines 196.

In the embodiment shown in FIG. 8, the local utilization circuits 24A, 24B and 24C, have, in part, been combined to provide only a single service call light 200 for the three stations controlled by each local decoder 30. Of course, this system according to the invention can include separate service call lights for each station, if desired. Further, said local utilization circuits include a lamp 202 (202A, 2028 and 202C) for each station. Service call light 200 is driven through driver 204 and flip-flop 206 by data input logic 194. In like manner, each lamp 202 is driven through a bidirectional gate-controlled thyristor which completes the AC path for said reading lamp when gated on, said gating signal being derived from flip-flop 210 controlled by data input logic 194. The data input logic 194 of each local decoder is activated in its proper time frame, detects the state data stored in each time slot of that frame and transmits a signal to the specific service call light on lamp of its utilization circuit 24 associated with said time slot to set the state of said call light or lamp. The group of local coders and the group of decoders are each in series connection for the purposes of sequential shifting. The correct local code and decoder are simultaneously activated during each frame, for example, local coder 28B and local decoder 308.

The above-described arrangement permits both the local coders and local decoders to be interchangeable among themselves since special circuitry is not required for each station to identify the local control or utilization circuit associated with that station, while full multiplexing is accomplished. This feature offers substantial advantages in terms of the number of types of equipment that must be maintained on inventory and convenience of maintenance. Said local coders and decoders are preferably adapted to be bidirectional by providing appropriate gating in timing counters 186 and 194 so that the system is operative if the column timer 26 were connected at the other end of the series connection of said local coders and decoders. If the system also incorporates supervisory control 40, the system timing is adjusted so that the data representative of the test functions and the supervisory call reset are detected after the data from each local coder 28 is latched so that the supervisory inputs would override the local control state date in all cases. In view of the switching speeds contemplated, the time gap between a particular data bit from the local coder and the overriding data bit from the supervisory control would be so slight as to be imperceptible.

While the supervisory control 40 provides some element of test capability to the system, a device for testing substantially the entire entertainment-service system would offer substantial advantages. To this end, a self-test circuit 220 is provided in each local control 22 as exemplified in FIG. 4, a 10-channel test signal generator is substituted for audio input 10 and a five-channel test signal is substituted for audio input 16. Said test signal generators are adapted to produce over each of the system audio channels a test signal of predetermined characteristics not normally present in the audio input signal. The test signal is preferably a tone of a frequency within the audiofrequency range to pass filters 104 and of sufficient strength to operate self-test circuit 220. The test signal generator may take any of the forms well known in the art and may be built into audio inputs 10 and 16. In such case, as shown in FIGS. 1 and 6, supervisory control 40 could.be provided with switch 166 to remotely activate the IO-channel test signal generator in audio input 10 by means of lines 167 and switch 168 to remotely activate the corresponding five channel test signal generator in audio input 16 by means of lines 169. The supervisory control incorporated in each of the other assemblies 8 would only incorporate switch 166 to control the test generator incorporated therein.

In its simplest form, said self-test circuit 220 is provided with a filter 222 connected to audio output line l10A-l and filter 224 connected to audio output line A-2. These filters are selected to pass only the frequency generated by said test signal generators and are connected to AND" gate 226 the output of which is connected to switch means 174. In the embodiment shown, switch means 174 is connected to manual lamp control 170 and adapted, in response to an output by AND" gate 226, to override said lamp control to produce a unique indication on line 176 equivalent to the repetitive opening and closing of said lamp control. If the entire system were operating properly, every lamp 202 in the system would blink in response to the signal so generated. To further extend the scope of the test on the system, self-test circuit 220 preferably includes a first transducer sense means 228 connected to the input side of transducer 128 and a second transducer sense means 230 connected to the input side of transducer 130. Each of said transducer sense means is adapted to provide an output to gate 226 when the coil of its corresponding transducer 128 and is intact, and therefore provides a low impedance to ground. However, if one or the other of said coils is broken, the resulting high impedance is sufficient to cut off the output of the corresponding transducer sense circuit so that the AND" gate 226 for that particular local control is not actuated and the corresponding lamp 202 does not blink.

If steps are taken to insure that at least one of each of the channel selector means 116 is set to each of the possible channels, the blinking or failure to blink of lamps 202 provides a test of substantially all of the system.

Thus, since each AND gate 226 requires the proper functioning of the two audio input channels and the two transducer coils associated therewith, it is apparent that substantially all of the entertainment portion of the system, including the entire main multiplexer and zone submultiplexer and substantially all of the local demultiplexers are tested. Further, since the output of the gate is connected to the service portion of the system, substantially all of the column timers, local coders, and local decoders are also tested. In this connection, it is noted that the lamps 202 arealso tested and that the balance of supervisory utilization circuit 38 and service call light 200 would be tested by the activation of the call light test switch 140 in supervisory control 40. Thus, by merely substituting test generators for audio inputs 10 and 16 the system performs an automatic self-test. This self-test results in substantial savings in time and labor and also provides a ready indication of the nature of any faults in the system through analysis of the particular lamps 202 which fail to blink.

Turning now to FIG. 5, a detailed circuit diagram of self-test circuit 220 is shown. The power supply for said self-test circuit is provided by tapping off audio output line 1 lA-2 and filtering the DC component from that output by means of resistor 240 and capacitor 241. A rectifying arrangement tapping off the audio output line can also be utilized. A positive voltage thus appears at terminal 242 and the bias voltages for the remainder of the circuit are obtained by connecting to said terminal. Filters 222 and 224 are substantially identical, consisting of series connected capacitors 244 shunted to ground by resistors 246 to define a first filtering stage and diodes 248 and resistors 250 shunted to ground by capacitors 252 and resistors 256 to define a second filtering stage. Transducer sense means 228 and 230 are defined by series connected resistors 256 connected to the base of transistors 258. The bases of said transistors are also connected through resistors 260 to bias voltage terminal 242 and to ground through capacitors 261. The collectors of said transistors are connected through resistors 262 to said bias voltage terminal while the emitters thereof are connected to ground. Transistors 258 are normally biased off. However, if a transducer coil is broken and a high impedance to ground appears at the input to transducer sense means 228 or 230, then the transistor 258 of that transducer sense means will be forced into conduction to close "AND" gate 226.

Said AND gate consists of diodes 264 connected respectively at their cathodes to the output of transducer sense means 228 and 230 (the collector of transistors 258), and resistor 270 connected at one end to the anodes of diodes 264 and 266 and, at its other end, to the bias voltage terminal 242. The output of AND gate 226 is connected to the input of switch means 174 represented by capacitor 270 shunted to ground and series connected resistor 272, which in turn is connected to the input of a stable multivibrator 274. Capacitor 270 provides a delay means for distinguishing the test signal from a portion of the regular audio input signal which might be of the test signal frequency. Said test signal frequency is preferably chosen from among those frequencies least likely to be present in normal audio programming. The test signal must be present for sufficient time to charge capacitor 270 to the triggering voltage of multivibrator 274, preferably about l5 seconds. Said triggering voltage provides still a further distinguishing characteristic of the test signal since a weak signal will be insufficient to trigger the multivibrator, and therefore to override the manual control of the corresponding lamp 202.

Said astable multivibrator includes transistors 276 and 277. The base of transistor 276 is connected to the cathode of diode 278, the base of which is connected through capacitor 279 to the collector of transistor 277. In like manner, the base of transistor 277 is connected to the cathode of diode 280 which in turn is connected to the collector of transistor 276 through capacitor 281. The base of transistors 276 and 277 are connected respectively through resistors 282 and 283 to ground. The emitters of said transistors are connected together, said common connection being connected through resistor 284 to ground. The collectors of said transistors are each connected through a resistor 285 and 286, respectively, to bias voltage terminal 242. The anode of diode 280 is connected to said bias voltage terminal through resistor 287, while the anode of diode 278 serves as the input to said multivibrator. The output of said multivibrator is taken at the collector of transistor 276 and is connected through resistor 288 to transistor 290.

The collector of transistor 290 is connected to output line 176 leading to the corresponding local coder. The emitter of said transistor is connected through resistor 291 to bias voltage terminal 242 and through resistor 292 to the movable arm of lamp control 170. Said movable arm is shunted to ground by means of resistor 293. The fixed terminal of lamp control is connected to the emitter of transistor 295, said emitter also being connected to ground through resistor 296. The base of transistor 295 is connected through resistor 297to the output of gate 226. The collector of said transistor is connected to the aforementioned line 176 which is shunted to ground by means of diode 298.

Switch means 174 operates as follows. When no test signal is detected, and the normal audio inputs 10 and 16 are applied, the manual closing of lamp control 170 turns on transistor 295 to present the appropriate signal to line 176, and therefore to the local coder. lf said lamp control is open, transistor 295 is turned off, also giving the appropriate indication to said local coder. Transistor 290 is in the off condition during this mode since its-base is returned to transistor 276 of astable multivibrator 274 which is normally off.

If a test signal is applied by means of a test signal generator, the detection of said test signal by the AND" gate, assuming all components of the system are functioning properly, produces a DC level at capacitor 270 proportional to the amplitude of said test signal. This positive level is coupled through resistor 297 to the base of transistor 295 to maintain said transistor in reverse biased condition for the duration of the test signal detection. This in effect disables the control function of lamp control 170, the signal passed along line 176 now being under the control of transistor 290 alone. This transistor follows the voltage levels of transistor 276 of multivibrator 274, alternating conduction and nonconduction with transistor 277 in the known manner. Accordingly, the signal at line 176 is an alternating signal which produces a blinking lamp in the corresponding utilization circuit to indicate a successful test. If a test signal is not detected, indicating some failure, the voltage of capacitor 270 is very nearly zero and the return path for the base of transistor 290 is through diodes 264 and 266 and the resistive path upstream thereof. In the latter case, the state of the lamp would be governed by lamp control 170 and would be steady.

If the entertainment-service system includes the special channel governed by PA selector switch 75, the activation of which overrides all other channels to apply the contents of said special channel to all of the headsets 20 without regard to the setting of channel selector switches 116, said special channel can be readily tested using the arrangement according to the invention. Testing can be accomplished by adapting the test signal generator to selectively apply a test signal different from the normal test signal to said channel while the normal test signal is applied to the balance of the channels. If the lamps 202 stop blinking and return to their normal state, the override feature of the special channel is operating properly. This results from the fact that the signal on the special channel is applied to all of the audio output lines instead of the normal test signal. Said special test signal can be of a different frequency which is not passed by filters 222 and 224 or of insufficient strength to trigger multivibrator 274. A separate switch can be provided in supervisory control 40 to apply the special test signal to the special channel after switches 166 and 168 are closed.

Self-test circuit 220 is shown disposed in local control 22 but could be disposed in either local coder 28 or local demultiplexer 18. While in the embodiment shown, the self-test circuit is connected to override lamp 202, this is merely shown by way of example and not limitation and any utilization circuit capable of indicating a successful test could be used for this purpose. Thus, service call lights 200 could be used as the alarm. Further, the unique test state of the utilization circuit providing test indication need not be the blinking state used in the embodiment shown. For example, if service call lights 200 are used and reset button 142 of supervisory control 40 is depressed before test, the lightingof said service call lights could provide the test indication.

The entertainment-service system according to the invention has many applications. For example, the system can be applied to an aircraft or other means of transportation where it is necessary for each seat to individually control entertainment functions by selectively choosing a plurality of channels and service functions such as reading lamps and service call lights to attract the attention of stewardesses. In such an application, the zone submultiplexers 14 might represent a compartment on the aircraft, each local decoder, each local coder and local demultiplexer being associated with a row of seats within that compartment, and each local utilization circuit and local control being associated with a particular seat within that row. The entertainment-service system according to the invention is particularly advantageous for use in aircraft where weight considerations are of critical importance, since the multiplexing techniques used herein result in substantial savings in weight. Further, the self test circuit expedites servicing time, therefore minimizing the downtime of an extremely valuable aircraft. Still other applications of the system according to the invention include, but are not limited to use in hospitals, intercom systems in buildings and all other circumstances wherein a plurality of remote stations are to be tied to a single entertainment-service system.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description are efficiently obtained, and, since certain changes may be made in the above constructions without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention; which, as a matter of language, might be said to fall therebetween.

lclaim:

1. In an entertainment-service system for a plurality of discrete stations including multiplexing means normally connected to a multichanneled source of audio input and adapted to sequentially sample each 'of said channels and transmit the content of said channels as a single signal; a plurality of remotely located demultiplexer means for receiving said single multiplexed signal; at least one control means disposed at each of said stations and associated with one of said demultiplexer means including channel selector means and utilization control means, at least one transducer means for converting an audio electrical signal to sound disposed at each station, said demultiplexer means each being adapted to reconstruct from the multiplexed signal the contents of the input channels selected by the channel selector means associated therewith and transmit same through an output to the corresponding transducer means; a plurality of remotely located utilization circuits, at least one of said utilization control means being associated with each of said utilization circuits; a plurality of coder means for detecting the state of the utilization control means associated therewith and for transmitting a signal representative of said state; and decoder means associated with each coder means for receiving said signal representative of the state of the corresponding utilization control means for controlling the state of the corresponding utilization circuits, whereby each of said utilization circuits is placed in a state responsive to the state of its corresponding utilization control means, the improvement which comprises, a multichannel test signal generator connected to said multiplexing means to apply a test signal of a predetermined characteristic to each input channel; and at least one self-test circuit means connected to the output of each demultiplexer means to detect the presence of said test signal and adapted to override, in response to said detected test signal, at least one utilization control means to produce a predetermined state indication for detection by the corresponding coder means, whereby the corresponding utilization circuits are disposed in said predetermined state.

2. The arrangement as recited in claim 1, wherein at least one of said self-test circuit means is provided for each of said control means, each of said self-test circuit means being connected to the output of the demultiplexer means associated with its control means.

3. An arrangement as recited in claim 2-, wherein at least one of said channel selector means is set to select each of said input channels.-

4. An arrangement as recited in claim 1, wherein said test signal is of a predetermined frequency, said self-test circuit means includingfilter means adapted to pass a signal substantially of said test signal frequency, and switch means responsive to said passed signal for overriding a corresponding utilization control means.

5. An arrangement as recited in claim 4, wherein said switch means is adapted to override said corresponding utilization control means only after a predetermined period during which said test signal is passed thereto.

6. An arrangement as recited in claim 1, wherein said test signal is of a predetermined frequency, each demultiplexer means output including first and second audio output lines for each transducer means, said self-test circuit means including first and second filter means connected respectively to said first and second audio output lines and adapted to pass a signal substantially of said test signal frequency, an AND" gate connected to said first and second filter means to receive the passed signals thereof, and switch means connected to the output of said "AND" gate for overriding a corresponding utilization control means in response to an output signal from said AND" gate.

7. An arrangement as recited in claim 6, wherein said switch means includes first and second transistors each having an emitter, a collector and a base, astable multivibrator means having an input and an output, and an output line for connection to the corresponding coder means, said utilization control means being in series connection with the emitter-collector path of said first transistor and said output line, said first transistor being normally conducting and having its base connected to receive the signal of said AND gate for biasing off in response to said signal, the emitter-collector path of said second transistor being in series connection with said output line in parallel to the series connection of said utilization control means and the emitter-collector path of said first transistor, said second transistor being normally off and having its base connected to the output of said astable multivibrator means, the input of said astable multivibrator means being connected to receive the signal of said AND gate.

8. An arrangement as recited in claim 1, wherein the corresponding transducer means are provided with first and second coils each adapted for separate sound transmission, said self-test circuit means being further adapted to produce a further signal if both of said coils are whole, and to override the corresponding utilization control means only upon detection of both the test signal at the demultiplexer output and said further signal representative of the condition of said transducer coils.

9. An arrangement as recited in claim 1, wherein said demultiplexer means output is provided with first and second audio output lines for each transducer means, the corresponding transducer means being provided with first and second coils adapted for separate sound transmission for connection to said first and second audio output lines respectively, said test signal being of a predetermined frequency, said self-test circuit means including first and second filter means connected respectively to said first and second audio output lines and adapted to pass only a signal substantially of said test signal frequency, first and second transducer sense means being connected respectively to said first and second transducer coils and adapted to procure a signal if said transducer coils are whole, an AND gate for receiving the passed signal of said first and second filter means and the signal of said first and second transducer sense means, and switch means responsive to the output of said AND gate for overriding a corresponding utilization control means.

10. An arrangement as recited in claim 9, wherein each of said transducer sense means includes a transistor having an emitter, collector and base, said transistor being normally biased off, an input to said AND" gate being in series connection with the emitter-collector path of said transistor and ground, said base being connected to said transducer coil for biasing of said transistor on and bringing said gate input to ground, if said transducer coil is broken.

11. An arrangement as recited in claim 1, wherein said selftest circuit means is adapted to produce a unique state indication for detection by the corresponding coder means, whereby the corresponding utilization circuits are disposed in said unique state.

12. An arrangement as recited in claim 11, wherein said unique state indication corresponds to the state indication which would be produced if said utilization control means were alternately turned on and off, whereby the corresponding utilization circuits are alternately rendered operative and inoperative when said test signal is detected.

13. An arrangement as recited in claim I, wherein said entertainment-service system includes means for selectively activating one of said input channels and means, responsive to said channel activation means, for applying to all of said transducer means the contents of said one channel without regard to the setting of said channel selection means, said test signal generator being adapted to selectively apply to said one channel a second test signal of characteristics different from said predetermined test signal, whereby said utilization circuits are disposed in other than said predetermined state upon the application of said second test signal to said one channel while said first-mentioned test signal is applied to the remaining of said input channels. 

1. In an entertainment-service system for a plurality of discrete stations including multiplexing means normally connected to a multichanneled source of audio input and adapted to sequentially sample each of said channels and transmit the content of said channels as a single signal; a plurality of remotely located demultiplexer means for receiving said single multiplexed signal; at least one control means disposed at each of said stations and associated with one of said demultiplexer means including channel selector means and utilization control means; at least one transducer means for converting an audio electrical signal to sound disposed at each station, said demultiplexer means each being adapted to reconstruct from the multiplexed signal the contents of the input channels selected by the channel selector means associated therewith and transmit same through an output to the correSponding transducer means; a plurality of remotely located utilization circuits, at least one of said utilization control means being associated with each of said utilization circuits; a plurality of coder means for detecting the state of the utilization control means associated therewith and for transmitting a signal representative of said state; and decoder means associated with each coder means for receiving said signal representative of the state of the corresponding utilization control means for controlling the state of the corresponding utilization circuits, whereby each of said utilization circuits is placed in a state responsive to the state of its corresponding utilization control means, the improvement which comprises, a multichannel test signal generator connected to said multiplexing means to apply a test signal of a predetermined characteristic to each input channel; and at least one self-test circuit means connected to the output of each demultiplexer means to detect the presence of said test signal and adapted to override, in response to said detected test signal, at least one utilization control means to produce a predetermined state indication for detection by the corresponding coder means, whereby the corresponding utilization circuits are disposed in said predetermined state.
 2. The arrangement as recited in claim 1, wherein at least one of said self-test circuit means is provided for each of said control means, each of said self-test circuit means being connected to the output of the demultiplexer means associated with its control means.
 3. An arrangement as recited in claim 2, wherein at least one of said channel selector means is set to select each of said input channels.
 4. An arrangement as recited in claim 1, wherein said test signal is of a predetermined frequency, said self-test circuit means including filter means adapted to pass a signal substantially of said test signal frequency, and switch means responsive to said passed signal for overriding a corresponding utilization control means.
 5. An arrangement as recited in claim 4, wherein said switch means is adapted to override said corresponding utilization control means only after a predetermined period during which said test signal is passed thereto.
 6. An arrangement as recited in claim 1, wherein said test signal is of a predetermined frequency, each demultiplexer means output including first and second audio output lines for each transducer means, said self-test circuit means including first and second filter means connected respectively to said first and second audio output lines and adapted to pass a signal substantially of said test signal frequency, an ''''AND'''' gate connected to said first and second filter means to receive the passed signals thereof, and switch means connected to the output of said ''''AND'''' gate for overriding a corresponding utilization control means in response to an output signal from said ''''AND'''' gate.
 7. An arrangement as recited in claim 6, wherein said switch means includes first and second transistors each having an emitter, a collector and a base, astable multivibrator means having an input and an output, and an output line for connection to the corresponding coder means, said utilization control means being in series connection with the emitter-collector path of said first transistor and said output line, said first transistor being normally conducting and having its base connected to receive the signal of said ''''AND'''' gate for biasing off in response to said signal, the emitter-collector path of said second transistor being in series connection with said output line in parallel to the series connection of said utilization control means and the emitter-collector path of said first transistor, said second transistor being normally off and having its base connected to the output of said astable multivibrator means, the input of said astable multivibrator means being connected to receive the signal of said ''''AND'''' gate.
 8. An arrangement as recited in claim 1, wherein the corresponding transducer means are provided with first and second coils each adapted for separate sound transmission, said self-test circuit means being further adapted to produce a further signal if both of said coils are whole, and to override the corresponding utilization control means only upon detection of both the test signal at the demultiplexer output and said further signal representative of the condition of said transducer coils.
 9. An arrangement as recited in claim 1, wherein said demultiplexer means output is provided with first and second audio output lines for each transducer means, the corresponding transducer means being provided with first and second coils adapted for separate sound transmission for connection to said first and second audio output lines respectively, said test signal being of a predetermined frequency, said self-test circuit means including first and second filter means connected respectively to said first and second audio output lines and adapted to pass only a signal substantially of said test signal frequency, first and second transducer sense means being connected respectively to said first and second transducer coils and adapted to procure a signal if said transducer coils are whole, an ''''AND'''' gate for receiving the passed signal of said first and second filter means and the signal of said first and second transducer sense means, and switch means responsive to the output of said ''''AND'''' gate for overriding a corresponding utilization control means.
 10. An arrangement as recited in claim 9, wherein each of said transducer sense means includes a transistor having an emitter, collector and base, said transistor being normally biased off, an input to said ''''AND'''' gate being in series connection with the emitter-collector path of said transistor and ground, said base being connected to said transducer coil for biasing of said transistor on and bringing said gate input to ground, if said transducer coil is broken.
 11. An arrangement as recited in claim 1, wherein said self-test circuit means is adapted to produce a unique state indication for detection by the corresponding coder means, whereby the corresponding utilization circuits are disposed in said unique state.
 12. An arrangement as recited in claim 11, wherein said unique state indication corresponds to the state indication which would be produced if said utilization control means were alternately turned on and off, whereby the corresponding utilization circuits are alternately rendered operative and inoperative when said test signal is detected.
 13. An arrangement as recited in claim 1, wherein said entertainment-service system includes means for selectively activating one of said input channels and means, responsive to said channel activation means, for applying to all of said transducer means the contents of said one channel without regard to the setting of said channel selection means, said test signal generator being adapted to selectively apply to said one channel a second test signal of characteristics different from said predetermined test signal, whereby said utilization circuits are disposed in other than said predetermined state upon the application of said second test signal to said one channel while said first-mentioned test signal is applied to the remaining of said input channels. 